Nanoscale microstructure and magnetic properties of melt-spun Sm(Co0.725Fe0.1Cu0.12Zr0.04B0.015)7.4 ribbons

We have investigated the nanocrystalline microstructure and the hard magnetic properties Of Sm(CO0.725Fe0.1Cu0.12Zr0.04B0.015)(7.4) melt-spun ribbons. The coercivity (H-c) of the as-spun ribbons increased with the wheel surface speed from 2.8kOe for 10m/s to 14.5kOe for 40m/s. The post-annealing of the melt-spun ribbons from 700 to 900 degrees C for 10 min did not lead to a substantial increase of Hc. However, after isothermal aging at 820 degrees C and subsequent slow cooling (0.5 degrees C/min) to 120 degrees C, H-c increased from 2.8 to 10.9kOe for 10m/s, while it decreased from 14.5 to 13.5kOe for 40 m/s ribbons. The grain size of the melt-spun ribbon reduced with structural transformation from 2:17H (Th2Ni17-hexagonal type) to 1:7H (TbCu7-hexagonal type) as the wheel surface speed was increased. Three-dimensional atom probe analysis showed a boron enriched precipitate at the grain boundaries in the as-spun ribbons, which acts as the grain growth inhibitor causing the refinement of the microstructure. (c) 2004 Elsevier B.V. All rights reserved.